The word 'speedster' is a modern English compound, formed by combining the native English noun 'speed' with the agent suffix '-ster'. The term 'speed' itself originates from Old English 'spēd', which initially meant 'success' or 'prosperity', a sense preserved in 'Godspeed'. Over time, its meaning narrowed to focus on the rapidity with which success is achieved, eventually specializing to mean 'swiftness of motion'. The suffix '-ster', from Old English '-estre', was originally used to form feminine agent nouns (e.g., 'spinster'). It later lost its gendered specificity and became a productive suffix for creating informal nouns denoting a person involved in a particular activity, often with a hint of familiarity or derision. Thus, a 'speedster' logically denotes a person or thing characterized by speed, a formation perfectly transparent to modern English speakers.

Structure: speed (fast movement) + ster (person associated with) - speed: From Old English 'spēd' (success, prosperity, quickness). In this compound, it carries the sense of 'fast movement'. - ster: From Old English '-estre', a feminine agent suffix, which evolved into a general agent suffix denoting a person associated with an activity or thing.